1. Field of the Invention
The present invention relates generally to microfilters and, in particular, to a method for making a microfilter using a supercritical fluid mixture to selectively remove soluble portions of a filter material composite thus forming micropores in the matrix or to add a filter material from the supercritical fluid mixture to a porous matrix forming the microfilter.
2. Description of Related Art
Filtration devices are used in a variety of industrial fields ranging from the electronics industry to the pharmaceutical industry. Depending on the application, the filter properties distribution and control of the pore size affects the relative filtration rate, durability and chemical and mechanical resistance. For convenience, the following description will be related to the electronics industry, and in particular, to the use of microfilters in the fabrication of semiconductor devices.
Microfilters are used in a variety of applications in the fabrication of semiconductor devices including purification of waste streams, filtration of process streams, photoresist manufacturing and recirculation baths. With the continuing decrease in the size of semiconductor devices however, there is a need for microfilters having finer pore size and better control of the pore size.
It is known to form pores in filter substrates by leaching of a filler material in the filter material matrix. U.S. Pat. No. 3,281,511 discloses a filler such as sodium chloride which is mixed with a polymer to form a dough. The dough is sintered and the pores are formed by dissolving the sodium chloride filler material. Leach processes such as this, however, do not provide commercial microfilters which require finer pore sizes.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide methods for making microfilters.
It is another object of the present invention to provide methods for making microfilters using a subtractive process.
A further object of the invention is to provide methods for making microfilters using an additive process.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.